Time-out control apparatus, terminal unit, time-out control system and time-out procedure

ABSTRACT

The present invention is built on a time out control apparatus to control the time out when a packet is transferred between terminal units connected to different buses. In the time out control apparatus, delay measuring means measures the delay time required for a response packet to be received after a request packet is sent to a terminal unit (control unit) connected via a bus. Delay information list generating means generates a delay information list in which the delay times measured by the delay measuring means are related to the individual identification information on the respective terminal units. Information output means reads out the delay time from the delay information list in accordance with a request from the terminal unit and outputs the delay time to the terminal unit. This sets the delay time on the time out register of the terminal unit.

FIELD OF THE INVENTION

[0001] The present invention relates to a time out control apparatus toconnect a plurality of physically separated buses to each other, and atime out procedure in a time out control system.

BACKGROUND OF THE INVENTION

[0002] The IEEE1394 interface is known as digital interface to transfersuch multimedia information as images and voices at a high speed andreal-time between the digital cameras and the personal computers.

[0003] In this IEEE 1394, up to 63 terminal units (hereinafter referredto as nodes) can be connected to one bus, and the longest length ofcable that can connect any two nodes is 4.5 m. All the nodes that areconnected to the buses 102 of this IEEE 1394 have each a virtual addressspace—48-bit address space called CSR address—on a memory 300 built inthe terminal unit 100 as shown in FIG. 20—and communication between therespective nodes is effected by reading or writing in this addressspace. The node, in case a request packet requesting to read or write inanother node connected to the same bus is sent, sets the timer with avalue as timer value—a value set at a split time out register(SPLIT_TIMEOUT REGISTER) 310 (hereinafter referred to as time outregister) located at a specific place in the address space of the memoryof the own node. It is so arranged that in case the timer times outbefore a response packet is received from the destination node of therequest packet (hereinafter referred to as destination node), the sourcenode of the request packet (hereinafter referred to as source node) willdo necessary time out procedures as re-sending of the request packet.

[0004] With a value of 100 ms as initial value, the time out registercan be changed from the source node or another node connected to thebus. Generally, the change can be made beforehand within the limit notexceeding the maximum 8 seconds in case the time required for the sourcenode to send a response packet after receiving a request packet exceeds100 ms.

[0005] In case a number of terminal units are used on the IEEE 1394buses or terminal units are used more than 4.5 m away from a node, aplurality of buses will have to be connected. For connecting the busesto each other, such a bus bridge is needed as disclosed in the Japanesepatent application laid open under No. 11-55297 (U.S. patent applicationSer. No. 09/130,601).

[0006]FIG. 21 shows the relation between a bus bridge 101, two buses102, 103 and terminal units 100. In this bus bridge 101, when data istransferred from a specific node to another specific node, the nodeidentification (ID) and other necessary parameters at the source arereplaced by those at the destination, which makes it possible totransfer data between different buses. Here if, on the bus of the IEEE1394, a new node is connected to a specific bus or a node connected to aspecific node is cut off, the bus will be reset. Each time the bus isreset, new node ID's will be given in accordance with a specific rule.

[0007] In case, as set forth above, a plurality of IEEE 1394 buses areconnected using the bus bridge to transfer packets between the nodes,the bus bridge will do such procedures as switching from the bus ID ofthe request packet received from the source node to the bus ID of thebus connected to the destination node so as to send the packets. Also,the response packet received from the destination node is changed in busID, and sent to the source node.

[0008] In this case, too, the source node reads the time out registervalue of its own node the same way as above. With this value as timervalue, the timer is set. And in case the timer times out before aresponse packet is received from the node via the bus bridge, such errorprocedures are taken as re-sending the request packet.

[0009] In this connection, it may be suggested that the bus bridgeshould change in advance the time out register value of the transfersource node, on supposition that the time required to transfer therequest packet and transfer the response packet can exceed the time outdefault value. But it can happen that there are a plurality of nodesthat request the bus bridge to transfer the request packets. In theabove method, therefore, the bus bridge is to set all the time outregisters of transfer source node of request packets in advance, whichincreases the traffic volume and could hinder ordinary datacommunication.

[0010] Furthermore, the time required for the response packet to bereceived after the request packet is sent can be different depending onthe processing capacity of the transfer destination node and on thecondition of the destination node. However, each node has only one timeout register, and to avoid time out, the source node has to use themaximum timer value combined of the source node and the destinationnode. However, to use the same timer value for all transfers presents aprocessing efficiency problem.

[0011] Another problem is that since the bus bridge requires complicatedprocedures for transfer of the packets, the transfer source node timeout register has to set the time with consideration given to theoverhead needed for the bus bridge to transfer packets. Furthermore, incase packets are transferred between nodes via a plurality of busbridges, the overhead can further increase. In such a case, the timerequired for a response packet to be received after the request packetis sent can exceed the maximum value set on the time out register, whichcan hinder normal packet communication.

SUMMARY OF THE INVENTION

[0012] In view of the prior art described above, including thedisadvantages and deficiencies of the prior art, it is an object of thepresent invention to provide a bus control appartus, terminal units, buscontrol system and time out procedure in the bus control system in whichtime out procedures can be done efficiently in packet communication viaa bus bridge.

[0013] To effect the object of the invention, the following means areadopted. First, the present invention is built on a time out controlapparatus to control the time out when a packet is transferred betweenterminal units connected to different buses as shown in FIG. 1.

[0014] In the time out control apparatus, delay measuring means 110measures the delay time required for a response packet to be receivedafter a request packet is sent to a terminal unit (control unit) 117connected via a bus 102. Delay information list generating means 111generates a delay information list 112 in which the delay times measuredby the delay measuring means 110 are related to the individualidentification information on the respective terminal units. Informationoutput means 119 reads out the delay time from the delay informationlist 112 in accordance with a request from the terminal unit and outputsthe delay time to the terminal unit. This sets the delay time on thetime out register of the terminal unit.

[0015] In case the terminal unit is not capable of making a request tothe time out control apparatus for the delay time, the informationoutput means 119 reads out the delay time from the delay informationlist 112 when the delay information list 112 is prepared, and outputsthe delay time to the terminal unit.

[0016] Furthermore, two arrangements may be used in combination—one inwhich the terminal unit is capable of requesting the delay time of thetime out control apparatus and the other in which the terminal unit isnot capable of so doing.

[0017] It is so arranged that when a bus reset occurs, the delaymeasuring means 110 measures the delay time needed for a response packetto be received in answer to a request packet sent to acquire individualidentification information on the terminal unit, thereby generating thedelay time in the delay information list.

[0018] In addition, it is desired that the delay measuring means 110measures the delay time each time the request packets and responsepackets are transferred a number of times to renew the delay time in thedelay information list 112.

[0019] In the usual configuration, the time out control apparatus isbuilt in the bus bridge. This is not restrictive. The bus bridge may bea separate unit. It is desirable that the delay time includes theinternal processing time in the bus bridge required to transfer therequest and response packets.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Having summarized the invention, a detailed description of theinvention follows with reference being made to the accompanying drawingswhich form part of the specification, of which:

[0021]FIG. 1 is a block diagram showing the make-up of the time outcontrol apparatus according to the present invention.

[0022]FIG. 2 is a schematic diagram of a read request packet and a readresponse packet used in the present invention.

[0023]FIG. 3 is a schematic diagram of a write request packet and awrite response packet used in the present invention.

[0024]FIG. 4 is a delay information list in an embodiment of the presentinvention.

[0025]FIG. 5 is a diagram showing the receiving and processing flow ofthe time out control apparatus according to the present invention.

[0026]FIG. 6 is a diagram showing the equipment information collectionprocessing flow according to the present invention.

[0027]FIG. 7 is a diagram showing the delay information read flow of thetime out control apparatus according to the present invention.

[0028]FIG. 8 is a diagram showing the packet transfer processing flowaccording to the present invention.

[0029]FIG. 9 is a diagram showing the main processing flow of the timeout control apparatus according to the present invention.

[0030]FIG. 10 is a diagram showing the packet transfer request sendprocessing flow according to the present invention.

[0031]FIG. 11 is a diagram showing the timer value acquisitionprocessing flow of the time out control apparatus according to thepresent invention.

[0032]FIG. 12 is a diagram showing the packet transfer processing flowof a control unit according to the present invention.

[0033]FIG. 13 is a diagram showing the response packet of the controlunit according to the present invention.

[0034]FIG. 14 is a diagram showing the time out processing flow of thecontrol unit according to the present invention.

[0035]FIG. 15 is a diagram showing another equipment informationcollection processing flow of the time out control apparatus accordingto the present invention.

[0036]FIG. 16 is a diagram showing a first embodiment with a bus bridgeand a time out control apparatus separated according to the presentinvention.

[0037]FIG. 17 is a connection diagram of the time out control apparatusof a terminal unit not corresponding to the bus bridge.

[0038]FIG. 18 is a constitutional diagram of the time out controlapparatus of a terminal unit not corresponding to the bus bridge.

[0039]FIG. 19 is a flow diagram showing the time out control process ofa terminal unit not corresponding to the bus bridge.

[0040]FIG. 20 is a diagram showing the prior art connection of theterminal unit to the bus.

[0041]FIG. 21 is a diagram showing the prior art connection of theterminal unit using the prior art bus bridge.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042]FIG. 1 is a block diagram showing the system make-up of anembodiment and the main make-up of the bus bridge and the control unit.The embodiment will now be described with reference to the drawing.

[0043] First, the whole system is so made up that, as shown in FIG. 1,the first bus 102 and second bus 103 in which IEEE 1394 is used areconnected to the bus bridge 101 and terminal units are connected to thefirst bus 102 and second bus 103 as shown in FIG. 1. There will bedescribed the operation when a bus reset occurs in the first bus 102 inthat make-up. The same description is applicable to the operation when abus reset occurs in the second bus 103.

[0044] In case a bus reset occurs in the first bus 102, the respectiveterminal units connected to the bus send self identification (ID)packets to the bus bridge 101. This self ID packet contains physicalnode ID to identify the terminal units and corresponding transmissionrate.

[0045] The self ID packet is received by the first packet receivingmeans 104 of the bus bridge 101 (FIG. 5, Step S 1), and the type of thepacket is analyzed by the first packet analysis means 108 of the busbridge 101. If the packet received and analyzed by first packet analysismeans 108 is found to be a self ID packet, equipment informationcollection means 109 of the bus bridge 101 is informed of that, andequipment information collection procedure (Step S 5) is done thefollowing way.

[0046] The equipment information collection means 109 extracts thephysical node ID from the received self ID packet (FIG. 6, Step S 11),and sends a read request packet to read a configuration ROM (hereinafterreferred to merely as ROM) with the individual number peculiar to theterminal unit (node proper number) like the unit ID written therein withthe physical node ID as the destination, and receives its responsepacket, thereby collecting node proper number of the terminal unit.Then, when the request packet is sent, the equipment informationcollection means 109 registers the destination node ID (made up of thebus ID and the physical node ID of the first bus 102) with the delaymeasuring means 110. In addition, when the response packet is received,the node ID contained in the response packet is notified to the delaymeasuring means 110. The delay measuring means 110 measures the delaytime required from the registration of the node ID of the destinationand the time required for the response packet to be received from therequest packet after the request packet is sent. The measurement is madefrom the registration of the destination node ID to the notification ofthe time when the response packet is received (FIG. 6 Steps S 13→S 15).Furthermore, the delay measuring means 110 adds a specific internalprocessing time at the bus bridge 101 to the delay time measured asmentioned above (FIG. 6, Step S 16).

[0047] The delay information list generating means 111 prepares a delayinformation list 112 (FIG. 6, Step S 18) in which 1) the above-mentionednode ID, 2) virtual identifiers the bus bridge 101 gives individually toall the terminal units connected to the bus separately from the node ID,3) the bus identifiers also given individually to identify the buses, 4)the node proper number read from ROM and 5) the above-mentioned delaytime, are related to each other (FIG. 6, Step S 18). Here in case asecond or further bus reset occurs, the bus bridge 101 collectsinformation on the respective terminal units connected to the bus theabove-mentioned way and also works out the delay time.

[0048] Then, the delay information list 112 is searched according to thenode proper number. In case the appropriate information is found, thenode ID, the bus identifier and the delay time alone are renewed (FIG.6, Steps S 17→S 19). This way, the same node can always be shown usingthe same virtual identifier. It is noted that delay information list 112is located at a specific address in the address space on the memory andthe delay time written therein can be read out from the respectiveterminal units connected to said bus bridge 101 as will be describedlater.

[0049] The delay information list 112 is located at a specific addressin the address space 301 on the memory as shown in FIG. 4, for example,and is made up of a bus identifier 302, the node ID 303, the virtualidentifier 304, a timer part 307 to show the delay time by a 32-bittimer integral part 305 and a 32-bit timer decimal part 306, and a nodeproper number 308. These are present in the same number as the nodesconnected to the bus bridge 101. In this case, the least significant 16bits are effective in the timer integral part 305, and the time can beset at up to 255 seconds. In the timer decimal part 306, the mostsignificant 13 bits are effective. And the timer can be set by {fraction(1/8000)} seconds.

[0050] There will now be described the time out procedure when acontrolled unit 118, which is connected to the second bus 103, iscontrolled from the control unit 117 connected to the first bus 102.First, the operation of the control unit 117 will be explained.

[0051] In the initialization after power is applied, the control unit117 reads out the delay information list 112 on the bus bridge 101starting with the head and acquires a virtual identifier thatcorresponds to the node proper number of the controlled unit 118 (FIG.9, Steps S 61→S 64). Here, it is understood that the relation betweenthe control unit 117 and the controlled unit 118 is fixed, and thecontrol unit 117 knows the node proper number of the controlled unit118.

[0052] Then, the request packet from the control unit 117 is transferredto the information output means 119 from the first packet receivingmeans 104 of the bus bridge 101 by way of the first packet analysismeans 108. Here, a corresponding virtual identifier is acquired from thedelay information list 112, and at the same time, a response packet isgenerated and sent to the control unit 117 through the first packetsending means 105.

[0053] When sending a response packet to the controlled unit 118(sending of the packet transfer request) (FIG. 9, Step S 68), thecontrol unit 117 reads the delay information list 112 of the bus bridge101 on the basis of the virtual identifier of the controlled unit 118.Therefore, timer value acquisition means 124 of the control unit 117first sends to the bus bridge 101 a read request packet 201 as shown inFIG. 2(a) (timer value acquisition) (FIG. 10, Step S 71; FIG. 11, Step S81).

[0054] In this case, the node ID of the bus bridge 101 is specified forthe destination ID 203 of the read request packet 201. For the ID 208 atthe source, the node ID of the control unit 117 is specified. To bespecified for the type 206 is that the type of packet to identify thepacket is a request packet 201 to request the delay information list. Tothe head address 209, an address in the delay information list 112 isspecified on the basis of the virtual identifier of the controlled unit118. To size 210, a seize to read is specified. To a label 204, a valueto identify transaction is specified, to an rt 205 retry code and to anpri 207 the priority of packet.

[0055] Meanwhile, the bus bridge 101 receives the read request packet201 and does a procedure—which will be described later—to send a readresponse packet. By this, the timer value acquisition means 124 of thecontrol unit 117 acquires the delay time of the controlled unit 118(FIG. 11, Step S 82).

[0056] Then, the equipment control means 122 of the control unit 117prepares a response packet with the virtual identifier of the controlledunit 118 as destination ID (FIG. 12, Step S 91). A write request packet213 as shown in FIG. 3(a) is prepared which contains the response packetin the data part (payload part) (FIG. 12, Step S 92), and then sent tothe memory for transfer of the bus bridge 101 by packet send means 121(FIG. 12, Step S 93). Then, destination ID 203 of the destination of thewrite request packet 213, label 204, rt 205 and pri 207 and ID 208 atsource are identical with those of the read request packet 201. Also, tothe data 215, a request packet to be sent is specified, and for thedestination node ID of the request packet, the virtual identifier of thecontrolled unit 118 is used.

[0057] In sending the write request packet 213, a timer management means123 sets the timer on the basis of the delay time of the controlled unit118 acquired as mentioned above to normally receive a response packetfrom the controlled unit 118 corresponding to the response packet of thepayload part (FIG. 10, Step S 73).

[0058] Then, when a packet receive means 120 of the control unit 117receives a response packet from the controlled unit 118, the timermanagement means 123 clears the timer if the timer is not timed out(FIG. 13, Step S 101-S 102). And, a procedure is done according to theresponse packet (FIG. 13, Step S 103).

[0059] If the timer times out before the response packet is received,the control unit 117 does a time out procedure (FIG. 9, Step S 67) thefollowing way.

[0060] The control unit 117 re-sends response packets as mentioned above(FIG. 14, Steps S 113→S 114) within a predetermined number of times(FIG. 14, Steps S 111→S 112). In case a response packet is not receivednormally even if a request packet is re-sent a predetermined number oftimes (FIG. 14, Steps S 111→S 112), error procedures like initializationof the bus are done (FIG. 14, Step S 115).

[0061] Then, there will be explained the operation when the bus bridge101 receives a read request packet 201 of the delay information list 112from the control unit 117.

[0062] If the bus bridge 101 receives a read request packet 201 of thedelay information list 112 from the control unit 117 by the first packetreceiving means 104, the type of the packet is analyzed by the firstpacket analysis means 108 the same way as in the case of the self IDpacket. If the first packet analysis means 108 finds the received packetto be a read request packet 201 of the delay information list 112, thenthat is notified to the information output means 119 of the bus bridge101, and delay information procedures (FIG. 5, Step S 6) is done in thefollowing way.

[0063] The information output means 119 extracts the head address 209from the read request packet 201 (FIG. 7, Step S 31), and works out avirtual identifier of the controlled unit 118 (FIG. 7, Step S 32).Furthermore, the information output means 119 searches the delayinformation list by the virtual identifier to read out the delay time ofthe controlled unit 118 (FIG. 7, Step S 33). Then, a first packetsending means 105 sends the delay time to the control unit 117 using aresponse packet 202 as shown in FIG. 2(b).

[0064] In this case, the node ID of the control unit 117 is specified tothe destination ID 203 of the response packet 202, and the ID of the busbridge 101 is specified to the source ID 208. To a result 211, theresults is specified as to whether the procedure for the read requestpacket 201 is successful or not. To data 212, the read-out result value,that is, the delay time is specified. The label 204, rt 205, pri 207 andseize 210 are treated the same way as the read-out read request packet201.

[0065] In the following, there will be explained the operation when thebus bridge 101 receives a write request packet 213, a request to writeon the memory for transfer, from the control unit 117.

[0066] In the bus bridge 101, if the first packet receiving means 104receives the write request packet 213, a request to write on the memoryfor transfer, then the packet type is analyzed by the first packetanalysis means 108 as in the case of the self ID packet. If the firstpacket analysis means 108 finds that the received packet is a writerequest packet 213, a request to write on the memory for transfer, thewrite request packet is written on the memory for transfer. It is notedthat the memory for transfer may be part of the address space of thememory 300 or a memory exclusively for transfer. At the same time, aresponse packet 214 as shown in FIG. 3(b) is sent to the control unit117 by the first packet sending means 105. Also, a packet transferprocedure (FIG. 5, Step S 7), which will be described in the following,is done by a transfer means 115.

[0067] The first transfer means 115 extracts a response packet from thepayload part of the write request packet written on the memory fortransfer (FIG. 8, Step S 41). Then, the first transfer means 115 takesout the virtual identifier of the controlled unit 118 or the destinationID of the response packet, and searches the delay information list 112on the basis of the virtual identifier via the information output means119 to acquire the corresponding bus identifier and node ID (FIG. 8,Steps S 42→S 43). Furthermore, response packet with the bus identifierand node ID as destination is prepared and transferred to the secondpacket sending means 107 via internal bus 114 (FIG. 8, Step S 44).

[0068] The second packet sending means 107 sends the request packet tothe controlled unit 118 and receives a response packet from thecontrolled unit 118 through the second packet receiving means 106. Thisresponse packet uses the virtual identifier of the control unit 117 asan address and is contained in the payload part of the write requestpacket 213 the controlled unit 118 sends. Furthermore, the write requestpacket 213 is to be written on the memory for transfer. And the busbridge 101 that receives the write request packet 213 does a procedureto send the response packet to the control unit 117—the same procedureas in the case of the write request packet 213 that the control unit 117sends (FIG. 8, Step S 47).

[0069] Furthermore, the first transfer means 115 sends notice to thedelay measuring means 110 every time request packets received from thecontrol unit 117 are transferred a specific number of times. In thiscase, the delay measuring means 110 registers the destination node ID inthe same way as mentioned above (FIG. 8, Step S 46), and measures thedelay time requires for one response packet to be received after therequest packet is sent (FIG. 8, Step S 49). In addition, the delaymeasuring means 110 adds a specific internal processing time in the busbridge 101 to the delay time measured as mentioned above (FIG. 8, Step S50). According to the delay time thus worked out, the delay informationlist generating means 111 renews the delay time for the node ID (FIG. 8,Step S 51) and the number of transfers is initialized with 0 (FIG. 8,Step S 52).

[0070] It is all right if the delay time is not renewed every time aspecific number of transfers are effected. But renewing the delay timeas mentioned above makes it possible to provide the control unit 117with the optimum timer value against fluctuations in processing time dueto changes in the state of the controlled unit 118. The interval atwhich measurements are taken is prolonged in case it is desired todecrease the overhead to the bus bridge 101 or in case there is not muchchange in the processing time at the terminal unit to be connected to.On the other hand, the interval can be changed and shortened, in casethe overhead can be ignored or in case the processing time of theterminal unit to be connected changes frequently.

[0071] As set forth above, the control unit 117 acquires the delay timefrom the delay information list 112 of the bus bridge 101 and sets thetime as timer value, whereby it is possible to do an optimum time outprocedure corresponding to the fluctuation in processing time due to thechange in the state of every controlled unit.

[0072] Embodiment 2

[0073] In Embodiment 1, it is a prerequisite that the terminal unit isprovided with timer value acquisition means to acquire the timer valueand timer management means to manage the timer value. In reality,however, all the terminal units are not capable of acquiring the timervalue by themselves. It can happen that a terminal unit that acquiresthe time out value by itself and a terminal unit that cannot acquire thetime out value by itself are connected on a bus at the same time. Theterminal units that cannot acquire time out values cannot transfer apacket through the bus bridge. Therefore, the prerequisite is transferof packets between the terminal units connected to the same bus.

[0074]FIG. 15 shows the procedure for collection of equipmentinformation in such a case (corresponding to FIG. 6).

[0075] In the equipment information collection shown in FIG. 6, afterthe procedure for working out the delay time is completed (FIG. 6, StepS 16), the delay measuring means 110 prepares a response packet to readthe ROM unit directory in which the components of the terminal unit arewritten on the basis of the self ID, and transfers the response packetto the terminal unit. Thereby, the terminal unit side returns to the busbridge 101 a response to the request. Receiving this response, the delaymeasuring means 110 can judge if the terminal unit is equipped with thetimer value acquisition means and timer management means. The judgementis notified to the delay information list generating means 111. And inthe writing procedure (FIG. 15, Step S 18), the delay information listgenerating means 111 writes—whether the terminal unit is a terminal unitwhere the time out value is written or not (flag) in the delayinformation list 112 by relating the proper identification informationon the respective terminal units 117—or renews.

[0076] When preparation or renewal of the delay information list 112 iscompleted, notice to the effect that “a delay information list isprepared (renewed)” is served from the delay information list generatingmeans 111 to the information output means 119, and at the same time theself ID is handed over. On receiving the notice, the information outputmeans 119 refers to the contents of the self ID and delay time list andjudges whether the terminal unit is a terminal unit requesting thewriting of the time out value (FIG. 15, Step S 180). Here, in case theterminal unit requires the writing of the time out value, the forecastmaximum value of the delay time to write is worked out, and its value isto be written on the time out register 310 of the terminal unitcorresponding to the self ID (FIG. 15, Steps S 181→S 182).

[0077] In the terminal unit not equipped with timer value acquisitionmeans, it is so arranged that the time-out value, first from the timeout control apparatus, is registered with the time out register 310. Insending the response packet, there is no read request.

[0078] Embodiment 3

[0079] The preceding embodiments are so constituted that a time outcontrol apparatus is built in a bus bridge that makes it possible totransfer packets between different buses. In the present invention,however, it is not always necessary to so form the time out controlapparatus and the bus bridge integrally. FIG. 16(a) shows arrangementsof a time out control apparatus separate from the bus bridge. FIG. 16(b)is its connection diagram. That is, the first bus 102 to which terminalunits 117 a, 117 b and 117 c are connected and the second bus 103 towhich terminal units 118 a, 118 b and 118 c are connected are connectedby a bus bridge 101A without a time out control function, and at thesame time, a bus bridge 101B is additionally connected between thebuses.

[0080] In the above arrangements, the process that the delay informationlist generating means 111 prepares a delay information list 112 iscommon to all the embodiments. But in this time out control apparatus,packets are not transferred. That is, it is so constituted that a firstrequest/response confirmation means 115 r and second request/responseconfirmation means 116 r are provided in place of the first transfermeans 115 and second packet transfer means 116.

[0081] In the above arrangements, the process to generate delayinformation list 112 (FIG. 6) and the read request process (FIG. 7) toacquire virtual identifier etc. of the controlled unit are identicalwith the above and will not be explained. The packet transfer process(FIG. 8) is effected by the bus bridge 101A, and there is no need forthe procedure to send response packets by the first transfer means 115(FIG. 8, Step S 44) and the procedure for sending a response packet(first half of S 47).

[0082] Furthermore, when receiving a destination node ID given by thefirst request/response confirmation means 115 r and the response packetfrom the destination node, the delay measuring means 110 measures thedelay time on the basis of the source node ID given from the secondrequest/response confirmation means 116 r and renews the delayinformation list 112.

[0083] The other details are identical with those of Embodiments 1 and2.

[0084] Embodiment 4

[0085] In Embodiments 1 and 2, the time out procedure between theterminal units are connected to two different buses. In the time outprocedure between the terminal units that can not be adapted for the busbridge (not provided with the timer value acquisition means 124), it ispossible to so constitute that the time out control apparatus isconnected on the bus with which terminal units are connected as shown inFIG. 17(a), (b).

[0086] That is such a case where the time out control apparatus 101C isconnected on the first bus 102 to which the terminal units 117 a, 117 band 117 c are connected or in case or such a state where the first busto which the terminal units 117 a, 117 b and 117 c and the second bus102 to which the terminal units 118 a, 118 b, 118 c are connected areconnected by the time-out control unit 101E (in this case, it isunderstood that the time-out control unit 101E is provided with a busconnection function and a time out control function corresponding to thebus bridge) and where a time out control unit 101C to control the timeout of the terminal units that can not be adapted for the bus bridge isconnected to the bus 102, and a time-out control unit 101D is connectedto bus 103.

[0087] The time-out control unit 101C or time-out control unit 101D inthat case are so constituted that there are provided only the elementscorresponding to only one of the buses as shown in 18.

[0088] In this arrangement, the equipment information collection when abus reset occurs is the same as the procedure shown in FIG. 15. Here,however, the time out control apparatus sees only packets flowing in thebus to which the time out control apparatus itself is connected, andtherefore no virtual identifier or bus identifier is needed.

[0089] Then, when a packet transfer request is issued from a specificterminal unit as shown in FIG. 19, delay time measurement is done. Thatis, the first packet analysis means 108 acquires source and destinationnode ID's from the sent packet and judges if the packet is a requestpacket from the control unit to the controlled unit (FIG. 19, Steps S201→S 202). If the packet is a request packet, the above-mentionedsource and destination node ID's are registered with the delay measuringmeans 110 (FIG. 19, Step S 203). Then, if the packet is judged to be aresponse packet in a judgement of the packet type, the delay measuringmeans 110 measures the delay time needed for the response packet toreturn from the controlled unit after the request packet is sent outfrom the control unit (FIG. 19, Step S 204).

[0090] Here, it is judged if the delay time thus measured is larger orsmaller than the maximum delay time in the delay time list firstprepared. If the delay time is smaller, then the contents in the delayinformation list generating means 111 will be re-written according tothe value thus obtained by the measurement (FIG. 19, Steps S 205→S 211).

[0091] In case the delay time thus measured is larger than the maximumdelay time in the delay time list first generated, time out less occursif a measured value is adopted, and therefore the contents in the timeout register 310 are renewed or replaced with the value obtained above,and the contents in the delay information list generating means 112 isrewritten (see FIG. 19, Steps S 206-S 210→S 211).

[0092] In the configuration shown in FIG. 17, a packet transfer from aspecific terminal unit and another specific terminal unit on the samebus may be effected through the transfer means 115 c indicated by dottedline in FIG. 18 if those two terminal units can acquire time-out valuesby themselves. Or whether the terminal units can acquire time-out valuesby themselves or not, the packet may be directly transferred between theterminal units.

[0093] Furthermore, the judgement whether “time out write judgement isON” (FIG. 15, Step S 180; FIG. 19, Step S 207) shown in FIG. 15 and FIG.19 judges if the object terminal unit corresponds to the bus bridge.That is, in case the terminal unit corresponds to the bus bridge, therewill be no need of time out writing (FIG. 15, Step S 182; FIG. 19, StepS 208).

[0094] While the bus bridge of IEEE 1394 only has been described, thepresent invention is not limited thereto but is applicable to a busbridge having a similar function.

[0095] In the present invention as set forth above, the bus bridgeconnecting a plurality of buses measures delay times required fortransfer of packets, which are provided as a list. The terminal unitcapable of acquiring the delay time thus provided reads the timer valuefrom the list on to the time out register and sets this timer value onthe timer for receiving the response packet. Thus, without setting atimer value longer than necessary, time out procedure can be doneefficiently.

[0096] In the terminal unit not capable of acquiring the delay time, itis so arranged that the timer value is written on the time out registerof the terminal unit from the bus bridge.

[0097] Also, by measuring the delay time every time packets aretransferred through the bus bridge a specific number of times, it ispossible to provide the optimum timer value corresponding to fluctuationin processing time due to the change in the state of the destinationterminal unit.

[0098] Furthermore, by including in the delay time the internalprocessing time required for the bus bridge to be transferred, it ispossible to provide a real timer value to the terminal unit requiringthe transfer of a packet.

What is claimed is:
 1. A time out control apparatus for control of timeout in transfer of packets between terminal units connected to differentbuses, said apparatus comprising: delay measuring means for measuringthe delay time required for a response packet to be received after thesending of a request packet to a terminal unit connected via a bus;delay information list generating means for generating a delayinformation list by relating proper identification information on therespective terminal units connected via a bus to the delay time measuredby said delay measuring means; and, information outputting means forreading out delay time from said delay information list in accordancewith a request from the terminal unit and outputting said delay time tosaid terminal unit.
 2. A time out control apparatus for control of timeout in transfer of packets between terminal units connected to differentbuses, said apparatus comprising: delay measuring means for measuringthe delay time required for a response packet to be received after thesending of a request packet to a terminal unit connected via a bus;delay information list generating means for generating a delayinformation list by relating proper identification information on therespective terminal units connected via a bus to the delay time measuredby said delay measuring means; and, information outputting means forreading out the maximum value of the delay time from said delayinformation list when said delay information list is generated andoutputting said value to the terminal unit, and reading out the delaytime from said delay information list in accordance with a request fromsaid terminal unit and outputting said delay time to said terminal unit.3. The time out control apparatus as defined in claim 1 or 2 whereinsaid delay measuring means generates delay time in said delayinformation list by measuring delay time required to receive a responsepacket in answer to a request packet sent to acquire properidentification information of said terminal unit in initializing thebus.
 4. The time out control apparatus as defined in claim 1 or 2wherein said delay measuring means measures said delay time every timerequest packets and response packets are transferred a specific numberof times, and the delay time in said delay information list is renewed.5. The time out control apparatus as defined in claim 1 or 2 whereinsaid delay time includes the internal processing time in a bus bridge tomediate said different buses, said time required for transfer of saidrequest packets and response packets.
 6. The time out control apparatusas defined in claim 1 or 2 which is provided inside the bus bridgemediating different buses.
 7. A time out control apparatus for controlof time out in transfer of packets between terminal units connected todifferent buses, said apparatus comprising: timer value acquisitionmeans for acquiring the delay time required for a response packet to bereceived after the sending of a request packet to the other terminalunit held in the time out control apparatus when the packets are sent tothe other terminal unit connected via the bus, timer management meansfor management of time out processing in transferring the packets on thebasis of said delay time acquired from said time out control apparatus.8. A time out control system for control of time out in transfer ofpackets between terminal units connected to different buses, the timeout control apparatus provided with: delay measuring means for measuringdelay time required for a response packet to be received after a requestpacket is sent to the terminal unit; delay information list generatingmeans for generating said delay information list by relating properidentification information of the respective terminal units connectedvia the bus to the delay time measured by said delay measuring means;and, information outputting means for reading delay time from said delayinformation list in accordance with a request from said terminal unitand outputting said delay time to said terminal unit; and, said terminalunit provided with: timer value acquisition means for acquiring delaytime of said other terminal unit from said time out control apparatuswhen a packet is sent to said other terminal unit connected via saidbus; and, timer management means for doing time out procedures intransferring said packet on the basis of said delay time acquired fromsaid time out control apparatus.
 9. A time out control system forcontrol of time out in transfer of packets between terminal unitsconnected to different buses, the time out control apparatus providedwith: delay measuring means for measuring delay time required for aresponse packet to be received after a request packet is sent to theterminal unit; delay information list generating means for generatingsaid delay information list by relating proper identificationinformation of the respective terminal units connected via the bus tothe delay time measured by said delay measuring means; and, informationoutputting means for reading out the maximum value of the delay timefrom said delay information list when said delay information list isgenerated and outputting said value to the terminal unit and for readingout the delay time from said delay information list in accordance with arequest from said terminal unit and outputting said delay time to saidterminal unit; and, said terminal unit provided with: timer valueacquisition means for acquiring delay time of said other terminal unitfrom said time out control apparatus when a packet is sent to said otherterminal unit connected via said bus; and, timer management means fordoing time out procedures in transferring said packet on the basis ofsaid delay time acquired from the time out control apparatus.
 10. A timeout control method for the time out control system to control the timeout in transfer of packets between terminal units connected to differentbuses, said method comprising: generating delay information list byrelating the delay time required for a response packet to be receivedafter the sending of a request packet to the terminal unit in said timeout control apparatus to proper identification information of therespective terminal units connected via said bus; and, said terminalunit doing time out procedure in transferring packets on the basis ofdelay time in said delay information list.
 11. The time out controlmethod as defined in claim 10 wherein said delay time is acquired by theterminal by itself.
 12. The time out control method as defined in claim10 wherein the maximum value of the delay time registered in the delayinformation list now is set in the terminal unit by the time out controlapparatus.
 13. A time out control apparatus for control of time out intransfer of packets between terminal units connected to the same bus,said apparatus comprising: delay measuring means for measuring the delaytime required for a response packet to be received after the sending ofa request packet to a terminal unit connected via a bus; delayinformation list generating means for generating a delay informationlist by relating proper identification information for respectiveterminal units connected via a bus to the delay time measured by saiddelay measuring means; and, information outputting means for reading outthe maximum value of the delay time from said delay information listwhen said delay information list is generated and outputting said valueto the respective terminal units.
 14. A time out control apparatuswherein said delay measuring means generate said delay information listby measuring the delay time required for a response packet to bereceived after the sending of a request packet to acquire properidentification information on said respective terminal units when saidbus is initialized.